Insulating fluid and methods for preparing and insulating concentric piping

ABSTRACT

The present inventions include an insulating fluid comprising a non-particulate viscosifying polymer, a water or brine, a cross-linking agent, and insulating particulates. The insulating fluid may be produced by performing the following steps in any order: adding a non-particulate viscosifying polymer to a brine, adding a cross-linking agent, adding insulating particulates, and optionally adding a solvent. The insulating fluid may be injected into an annulus surrounding a pipe such as production tubing, casing, surface pipelines, subsea pipelines, or risers.

FIELD OF INVENTION

The present inventions relate to an insulating fluid, a method for preparing the insulating fluid, and a method for insulating concentric piping using the insulating fluid.

BACKGROUND

Annular fluids or packer fluids are liquids that are pumped into an annular opening between a casing and a wellbore wall or between adjacent, concentric strings of pipe extending into a wellbore. The main functions of a packer fluid are to provide hydrostatic pressure in order to lower differential pressure across a sealing element, to lower differential pressure on the wellbore and casing to prevent collapse, and to protect metals in the completion from corrosion. Packer fluids are prepared according to the requirements of the given completion. Generally, they should be of sufficient density to control the producing formation, solids-free and resistant to viscosity changes over long periods of time, and non-corrosive to the wellbore and completion components.

Special well conditions may require a packer fluid to also serve an insulating function. In high temperature wells, hot fluid flowing inside the production tubing can cause the packer fluid to expand, rapidly building up pressure in the sealed annulus. In extreme circumstances, this build-up could potentially collapse the tubing or burst the casing, a result that would be catastrophic to the well. In addition, heat loss from the production tubing may cause a variety of low-temperature problems including hydrate build-up, paraffin deposition, and precipitation of salts.

Deepwater wells face a similar problem related to flow assurance. Undesired heat loss from production tubing to outer annuli can lead to the deposition of sludge, paraffin and asphaltene materials, the formation of gas hydrates, and cause severe flow assurance problems and loss of productivity. In recent years, thermal insulation fluids have been successfully applied in wellbore and deepwater risers to prevent undesired heat loss. Other alternatives include external insulation or injection of nitrogen gas for risers. Thus, many wells could benefit from the use of an insulating fluid capable of use in completions and risers.

US Published Application 2004/0011990 A1 (hereafter Dunaway) discloses a thermally insulating fluid comprising a glycol solvent for a viscosifier, a viscosifier, and optionally an aqueous brine. The glycol may be selected from a propelyne glycol, or under excessive heat temperatures, a butylenes glycol, which can be used with or without a viscosifier. Viscosifiers can be selected from hydroxyl propyl methyl cellulose, xanthan and hydroxyl propyl guar and combinations thereof. The Dunaway fluid is not as insulating as is often desired.

US Published Application 2005/0038199 A1 (hereafter Wang) discloses a thermal insulating fluid containing water and/or brine, a crosslinkable viscosifying polymer, a crosslinking agent and an optional set retarder. The composition is capable of inhibiting unwanted heat loss from production tubing or uncontrolled heat transfer to outer annuli. The viscosity of the composition is such as to reduce the convection flow velocity within the annulus. Although the insulating fluid in Wang exhibits low convection, the Wang fluid is not as insulating as is often desired.

US Published Application 2004/0059054 (hereafter Lopez) discloses a thermal insulating fluid containing at least one water superabsorbent polymer and optionally water and/or brine, and a viscosifying polymer. The composition is capable of inhibiting unwanted heat loss from production tubing or uncontrolled heat transfer to outer annuli. The viscosity of the composition is sufficient to reduce the convection flow velocity within the annulus. One of the potential drawbacks of using the fluid in Lopez is that when a workover is necessary, The Lopez fluid is not as insulating as is often desired.

There is a need in the industry for the development of a insulating fluid that exhibits low thermoconductivity, low convection, and thermal stability.

SUMMARY OF THE INVENTION

The present inventions include an insulating fluid comprising a non-particulate viscosifying polymer, a water or brine, a cross-linking agent, and insulating particulates.

In some embodiments, the present inventions include a method for insulating concentric pipes having an annulus, comprising injecting an insulating fluid in the annulus; wherein the insulating fluid comprises a non-particulate viscosifying polymer, a water or a brine, a cross-linking agent, and insulating particulates.

In other embodiments, the present inventions include a method for producing an insulating fluid comprising the following steps: adding a non-particulate viscosifying polymer to a brine, adding a cross-linking agent, and adding insulating particulates. The adding may be performed by continuous mixing or batch mixing; and steps (a) through (c) may be performed in any order.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is better understood by reading the following description of non-limitative embodiments with reference to the attached drawings, which are briefly described as follows:

FIG. 1 illustrates the test setup used for measuring the thermal conductivity of the insulating fluid.

FIG. 2 is a plot of the yield strength of the insulating fluid.

DETAILED DESCRIPTION

The invention relates to the application of a polymer-based fluid as an annular fluid (insulating fluid or packer fluid) for insulating production tubing or casing, insulating fluid during well treatment, or insulating fluid for risers for deepwater wells. This fluid is non-convective and exhibits low thermal conductivity and high thermal stability. The insulating fluid comprises a non-particulate viscosifying polymer, a water or brine, a cross-linking agent, and insulating particulates. Optionally, the insulating fluid may further comprise a solvent. The density of the fluid is adjustable to fit the downhole pressure requirement for the wells.

Preferred non-particulate viscosifying polymers are those having a high degree of molar substitution (MS) and are salt-tolerant. The hydroxyl groups enable better hydration in high concentration brines. Suitable non-particulate viscosifying polymers include cellulose, xanthan, starch, guar gum and a derivatives thereof. Particularly suitable viscosifying polymer fluids include hydroxyl propryl guar, carboxymethyl hydroxypropyl, and carboxymethyl-cellulose. The non-particulate viscosifying polymer is preferably present in a quantity of 0.1% to 5% by weight.

The fluid can be crosslinked by metal ions such as Zr or Ti crosslinkers. Crosslinking generally increases viscosity, which in turn reduces eliminates convection. If desired, the crosslinking can be delayed to ensure pumpability of the fluid during mixing and for an amount of time thereafter. Suitable cross-linking agents include borate, zirconium, and organic complexed metals. The cross-linking agent is present in a quantity of 0.01% to 5% by weight.

To lower the thermal conductivity and increase viscosity, particulates such as hollow glass bubbles, beads, or fibers are added to the mixture. The insulating particulates can be suspended in the mixture because of its high viscosity. Void spaces in the insulating particulates, if present, help reduce thermal conductivity of the mixture. The insulating particulates are preferably present in a quantity of 0.1% to 30% by weight.

Optionally, a solvent may be added to the insulating fluid to enhance the properties. Particularly suitable solvents include ethylene glycol ethers, propylene glycol ethers, and polyols.ethylene glycol ethers, propylene glycol ethers, and polyols. The solvent is preferably present in a quantity of 0.1% to 99.9% by weight.

Preferred methods for producing the present insulating fluids generally include: adding a non-particulate viscosifying polymer to a water or brine, adding a cross-linking agent; and adding insulating particulates. The insulating fluid may be mixed in the lab or in the field using a batch mixing method or continuous mixing method. The components of the insulating fluid may be mixed in any order. Optionally a solvent may be added to the mix via batch mixing or continuous mixing.

One preferred method of using the insulating fluid is for insulation of concentric piping, downhole tubulars, or similar situations where it is desirable to insulate the outside of a pipe. The insulating fluid may be injected into the annulus between two or more concentric pipes or between a pipe and a wellbore or the like. Applications in which the present insulating fluids may be used include, but are not limited to, outside of production tubing casing, between casing and tubing, and around surface pipelines, subsea pipelines, or risers.

Advantages of some embodiments of the invention include one or more of the following:

-   -   Low thermal conductivity     -   Non-convection     -   High thermal stability     -   Synergistic effect between cross-linking agent and insulating         particulates     -   High pumpability (can be continuously mixed)     -   Easily broken to remove from the concentric piping with acids,         peroxides, or other breakers     -   Environmentally safe

Examples Example 1

In Example 1, the thermal conductivity of various formulations of the insulating fluid were measured using a guarded heat flow meter. The guarded heat flow meter method is appropriate for measuring thermal conductivities in the range of 0.1 to 8 Wm⁻¹·K⁻¹ in the temperature range from −120 to 300° C. with an accuracy of approximately ±6%. This method is described in ASTM (American Society for Testing and Materials) Practice F 433, Standard Practice for Evaluating Thermal Conductivity of Gasket Materials and in ASTM E 1530, Standard Test Method for Evaluating the Resistance to Thermal Transmission of Thin Specimens of Materials by the Guarded Heat Flow Meter Technique.

A schematic diagram of the guarded heat flow meter is shown in FIG. 1. The sample (a 2.0 inch diameter disk) was placed between two plates at different temperatures, thus producing a heat flow through the sample. The hot-side heater temperature, T_(h), was controlled with a set-point controller; this parameter is used to set the mean temperature of the sample. The cold-side temperature and the guard temperature were controlled relative to the heater with differential controllers. The heat flow was measured with a heat flux transducer (a multi-junction thermopile across a thin sheet of insulation) contained in the lower plate. The sample was surrounded by a cylindrical guard which was maintained at a temperature close to the mean sample temperature to reduce lateral heat flow. Upper plate, lower plate, and guard temperatures were measured with type K (chromel/alumel) thermocouples. The sample was held between the plates of the instrument with a piston pressure on the order of 20 psi.

Four samples containing a base fluid, Zr as a cross-linking agent, hydroxyl propryl guar (HPG) as a non-particulate viscosifying polymer, and varying amounts of glass beads as insulating particulates were tested. Two of the four samples also included a solvent (propylene glycol). Comparative sample (0419-1) contained no insulating particulates. Table 1 shows the compositions of the tested formulations:

TABLE 1 Polymer Glass Beads Glass beads cross-linker Zr Sample wt % wt % (g/100 mL) wt % HPG Base fluid cross-linker A 0.94 3.30 4.2 0.20 100# 10.5 ppg NaBr 2 gpt B 0.88 9.56 13 0.20 100# 10.5 ppg NaBr 2 gpt C 1.05 11.30 13 0.20 100# 50/50 2% KCl and 2 gpt propylene glycol D 1.20 0 0.0 0.20 100# 50/50 2% KCl and 2 gpt propylene glycol

Each sample was tested at two temperatures and the thermal conductivity data was recorded. The results of the tests are displayed in Table 2 below:

TABLE 2 Thickness @ 25° c. Temperature Conductivity Conductivity Sample (mm) (° C.) (° F.) (W/m-K) BTU/(ft. h. ° F.) A 10.4 4 39 0.433 0.250 23 73 0.457 0.264 B 9.84 5 41 0.341 0.197 23 73 0.342 0.198 C 11.0 5 41 0.304 0.176 23 74 0.299 0.173 D 10.3 5 41 0.393 0.227 23 74 0.389 0.225

Example 2

In Example 2, a sample was tested using a rheometer to determine thermal convection from yield strength (or gel strength) data. The standard paper used for natural convection of a viscous fluid in an annulus is G. Paul Willhite, “Over-all Heat Transfer Coefficients in Steam and Hot Water Injection Wells,” Journal of Petroleum Technology, May, 1967, which is hereby incorporated by reference. There is an inverse correlation between gel strength and convection because insulating fluids can be modeled as Bingham materials. When a layer of Bingham material is subjected to a shear stress, it will not flow unless the shear stress exceeds the yield strength strength, τ₀. Therefore a fluid with high yield strength will exhibit low convection.

In this example, the formulation of the sample was the same as that of sample A in Example 1. The experiments were performed at 1 Hz of frequency with an oscillation rheometer at a temperature of 44° C. A 1 mm sample was placed in between two plates. The bottom plate was fixed and the upper plate was oscillated. The torque required to oscillate the plate was measured and the yield strength of the sample. The results are shown FIG. 2. The same test was performed for a non-convective oil-based packer fluid. Sample A exhibits much higher yield point than the packer fluid, which suggests that the sample A is non-convective.

Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials, and methods without departing from the scope of the invention. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as the latter are merely exemplary in nature. 

1. A method for insulating a length of pipe within an annulus, comprising injecting into the annulus an insulating fluid, wherein the insulating fluid comprises a non-particulate viscosifying polymer, a water or brine, a cross-linking agent, and insulating particulates.
 2. The insulating fluid of claim 1 wherein the insulating particulates are selected from the group consisting of microspheres, glass beads, and fibers.
 3. The method of claim 1 wherein the pipe is production tubing, casing, surface pipelines, subsea pipelines, or risers.
 4. The insulating fluid of claim 1 wherein the cross-linking agent is selected from the group of consisting of borate, zirconium, titanium and organic complexed metals.
 5. The method of claim 1 wherein the insulating fluid further comprises a solvent.
 6. The insulating fluid of claim 5 wherein the solvent is an ether.
 7. The insulating fluid of claim 6 wherein the ether is selected from the group consisting of ethylene glycol ethers, propylene glycol ethers, and polyols.
 8. The insulating fluid of claim 1 wherein the non-particulate viscosifying polymer is selected from the group consisting of cellulose, xanthan, starch, guar gum and a derivatives thereof.
 9. The insulating fluid of claim 8 wherein the a non-particulate viscosifying polymer is selected from the group consisting of hydroxyl propryl guar, carboxymethyl hydroxypropyl, and carboxymethyl-cellulose.
 10. The insulating fluid of claim 1 wherein the cross-linking agent is present in a quantity of 0.01% to 5% by weight.
 11. The insulating fluid of claim 1 wherein the non-particulate viscosifying polymer is present in a quantity of 0.1% to 5% by weight.
 12. The insulating fluid of claim 1 wherein the insulating particulates are present in a quantity of 0.1% to 30% by weight. 